Detergent compositions have long employed materials, known as "builders", to improve the detergency of soaps and synthetic detergents by actively chelating alkali metal cations which are normal components of "hard" tap water. Such builders have been found to affect, for instance, soil suspension, emulsification of soil particles, solubilization of waterinsolubles, and inactivation of various mineral constitutents present in a detergent system. Many materials useful as builders have been proposed, and their effects are known. See, e.g., U.S. Pat. Nos. 3,852,213, 3,950,260, 4,182,718, and 4,440,646 (all incorporated herein by reference).
Recently, however, the attention of detergent manufacturers and researchers has turned to the role of heavier metal cations, i.e., transition metal cations and particularly iron, in the formation of stain complexes on fabrics and other surfaces. It has been observed that these multivalent transition metal cations, particularly iron (Fe.sup.+++), enhance the binding of the components of many stains to substrates, and breaking up the cation-enhanced bonds is an effective approach to stain removal. Therefore, there is a strong need for the discovery of new materials that are effective as chelating agents for transition metal cations, are easy to prepare, and can be added to detergent compositions in economical amounts to boost stain-removing power.
It has now been discovered that carboxylic acid and hydroxamic acid-functional polymers can be easily and advantageously prepared from polyacrylic acid and that such polymers are active transition metal ion chelating agents, particularly with respect to iron (Fe.sup.+++), which makes these polymers extremely useful as stain removing agents that can be included in detergent compositions. The polymeric carboxy hydroxamic acids are most advantageously prepared by a process utilizing polyacrylic acid which is dehydrated to produce polyacrylic anhydride in a manner that is more efficient than previously known methods. The polyacrylic anhydride is then reacted with a hydroxylamine compound to produce the novel polymeric carboxy hydroxamic acids. The bi-functional nature of the polymeric product and the variability in the relative positions of the functional acid groups along the hydrocarbon chain make the polymeric carboxy hydroxamic acids especially effective as detergent additives or for any application where chelation of transition metal ions is desired.